Conversion of T4 to T3 and rT3 and their cytoplasmic binding: pH dependency

Höffken, B.; Ködding, R.; Hesch, R. D.

doi:10.1016/0009-8981(77)90314-x

Cited by 19 publications

(9 citation statements)

References 23 publications

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“…The pH optimum for T3 generation was found to be 6.5 which is very similar to that observed by others in rat liver homogenate (12) or rat liver microsomes (13). In contrast to these latter studies in which no rT3 generation could be detected at pH 6.5, this only being detected at -pH 9.0, we found significant quantities of rT3 at pH 6.5.…”

Section: Discussionsupporting

confidence: 89%

“…In this earlier work, the experimental conditions employed did not permit detection of either T3 or rT3 generation. In rat liver, on the other hand, the subcellular locus of T3 and rT3 generation has been reported to be associated with the microsomal fraction (9,13), although in rat kidney, it appears to be associated with a particulate fraction comprising plasma membranes and mitochondria (15). Recently, Maciel et al (25) have presented evidence suggesting that the plasma membrane fraction is the subcellular locus of T3-generating activity in rat liver.…”

Section: Discussionmentioning

confidence: 99%

“…rT3 generation from T4 has also been demonstrated in rat liver in vitro (12,13). 1 Abbreviations used in this paper: DC, disrupted cell preparation; DTT, dithiothreitol; MMI, methimazole; N, nuclear fraction; P, 27,000-g particulate fraction; PTU, propylthiouracil; rT3, L-reverse-T3; SI, initial 400-g supernate; S2, 27,000-g supernate; SH, sulfhydryl; T3, L-triiodothyronine; T4, L-thyroxine.…”

Section: Introductionmentioning

confidence: 96%

“…Radioimmunoassay, in addition to being more specific than chromatographic analysis, permits more precise quantification of the very small quantities of T3 generated. Using this approach, several investigators have reported the generation of T3 from added nonradioactive T4 by rat tissues in vitro and have examined some of the characteristics of the T3-generating system (9)(10)(11)(12)(13)(14)(15).…”

Section: Introductionmentioning

confidence: 99%

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l-Triiodothyronine and l-Reverse-Triiodothyronine Generation in the Human Polymorphonuclear Leukocyte

Woeber¹,

Maddux²

1978

J. Clin. Invest.

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A B S T R A C T Extrathyroidal monodeiodination of Lthyroxine (T4) is the principal source of L-triiodothyronine (T,) and L-reverse-triiodothyronine (rT,) production. To define some of the cellular factors involved, we examined T3 and rT3 generation from added nonradioactive T4 in human polymorphonuclear leukocytes, using radioimmunoassays to quantify the T3 an-d rT3 generated. Under optimumii incubation conditions which included a pH of 6.5 in sucrose-acetate bulffer, the presence of dithiothreitol as a sulfhydrylgroup protector, and incubation in an hypoxic atmosphere, significant net generation of T3 and rT3 was observed. Of the several subcellular fractions studied, the particulate fraction obtained by centrifugation at 27,000 g was found to possess the highest T3-and rT3-generating activities per unit quantity of protein. With respect to T3 generation from substrate T4, the K,m was 5 ,MNI and the Vmax was 7.2 pmol/min per mg protein. Propylthiouracil, methimazole, and prior induction of phagocytosis inhibited both T3 and rT3 generation, but T3 generation was inhibited to a greater extent. rT3, in a concentration equimolar to that of substrate T4, did not alter T3 generation, but inhibited T3 generation when the molar ratio of rT3 to T4 approached 10:1.Under the incubation coniditions employed, particulate fractions of leukocytes obtained fromn five cord blood samiples displayed an essentially normal relationship b)etween T3-and rT3-generating activities, despite the distinctly divergent serum T3 and rT3 concentrations in these samples. From our findings, we draw the following conclusions: (a) the human polymorphonuclear leukocyte possesses the ability to generate T3 and rT3 from substrate T4; (b) the T3-and rT3-generating activities are associated principally with the 27,000 g particulate fraction and display enzymic characteristics with a sulfhydryl-group requirement; (c) T3-generating activity appears to be more susceptible to inhibitory influences than rT3-generating activity; and (d) in cord

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Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

l-Triiodothyronine and l-Reverse-Triiodothyronine Generation in the Human Polymorphonuclear Leukocyte

Woeber¹,

Maddux²

1978

J. Clin. Invest.

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“…These findings are hard to interpret, since in the homogenate optimal conditions for the reactions will depend not only on the nature of the enzymic reaction but also on the availability of the substrates, since pH may be of importance in the binding of iodothyronines to cytoplasmic proteins (Hoffken et al, 1977). Nevertheless, conversion of thyroxine into tri-iodothyronine by rat liver microsomal fraction was also found to be maximal at pH6.0 (Hoffken et al, 1977;T. J. Visser, unpublished work).…”

Section: Resultsmentioning

confidence: 99%

Sequential deiodination of thyroxine in rat liver homogenate

Visser¹,

Fekkes²,

Docter³

et al. 1978

Biochemical Journal

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Rat liver homogenate was incubated at 37°C with thyroxine, 3,3',5-tri-iodothyronine, 3,3',5'-tri-iodothyronine or 3,3'-di-iodothyronine. The degradation or accumulation of these compounds was measured by specific radioimmunoassays. (1) Production of 3,3',5-tri-iodothyronine from thyroxine was highest at pH 6.0-6.5 and was markedly stimulated by the addition of dithiothreitol and effectively inhibited in the presence of 6-propyl-2-thiouracil. (2) Accumulation of 3,3',5'-tri-iodothyronine on incubation of thyroxine with homogenate was only observed above pH 8.5. Otherwise the product was converted into 3,3'-di-iodothyronine too rapidly to allow its measurement. By measuring 3,3'-di-iodothyronine it was deduced that 5-deiodination of thyroxine was most effective at approx. pH 8.0. Dithiothreitol powerfully stimulated this reaction and 6-propyl-2-thiouracil strongly inhibited. (3) Monodeiodination of the tyrosine ring of 3,3',5-tri-iodothyronine was the slowest reaction, was optimal at pH 8.0 and was less affected by dithiothreitol and 6-propyl-2-thiouracil than the above reactions. (4) 5'-

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Subcellular localization of thyroxine-5-deiodinase in rat liver

Brinke

Köhrle

Ködding

et al. 1980

J Endocrinol Invest

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L-Thyroxine (T4) is monodeiodinated to 3,3',5'-triiodothyronine (rT3) and 3,3',5'-triiodothyronine (T3). A recent work has demonstrated that T4-5'-deiodinase is localized solely in the microsomes of rat liver, as was originally suggested. In this study identical subcellular localization was also found for T4-5-deiodinase. This is in contrast with a previous report, indicating that T4-5-deiodinase is present in the soluble cytosol fraction of rat liver. Our results strongly indicate that the thyromimetically active T3 as well as the regulatory active rT3 are both formed from T4 in a microsomal enzyme complex.

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Conversion of T4 to T3 and rT3 and their cytoplasmic binding: pH dependency

Cited by 19 publications

References 23 publications

l-Triiodothyronine and l-Reverse-Triiodothyronine Generation in the Human Polymorphonuclear Leukocyte

l-Triiodothyronine and l-Reverse-Triiodothyronine Generation in the Human Polymorphonuclear Leukocyte

Sequential deiodination of thyroxine in rat liver homogenate

Subcellular localization of thyroxine-5-deiodinase in rat liver

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